1. Field of the Invention
This is a continuation-in-part of U.S. Pat. application Ser. No. 456,713, filed Dec. 26, 1989. This invention relates to an apparatus for the recovery of certain elements from a combustible liquid. More particularly, the invention concerns a continuous combustion apparatus for recovering in quantity the trace amounts of certain elements, such as iodine, present in crude oils.
2. Background
The age of orude oil found in a region is a significant parameter.in deciding where next to explore for crude oil in that region with a reasonable prospect of success. The age of the oil establishes a relationship between the oil and a possible source rock, i.e. where the oil potentially originated, as compared to where it was actually found since oil, being fluid, will migrate when certain geological conditions are present. Once the likely source rock is established, this is a factor in deciding where next to drill.
One of the methods of determining the age of crude oil is to use iodine-dating. Iodine is found in crudes in small, trace quantities. The radioactive isotope of iodine decays with time at a known rate to a stable, non-radiooactive isotope. The relative concentration of isotopes provides a basis for estimating the age of the crude oil. Thus, in order to measure or estimate crude oil age, it is essential to collect a sufficiently large sample of iodine from the crude oil to be abl to determine the relative quantities of iodine isotopes present with a reasonable degree of accuracy.
The existing chemical methods for recovering iodine from crude oil are complex, lengthy, tedious and require the attention of skilled chemists. These processes include such chemical means as liberating organically bound iodine by reaction with biphenyl sodium or complexing the iodine with mercury.
More recently, combustion techniques have found use in recovery of iodine and other elements from combustible compositions such as crude oil and coal. An article entitled "Determination of Volatile Elements in Coal and Other Organic Materials," American Laboratory, August, 1981, explains how to use a combustion bomb, the "Parr bomb," to analyze for specific elements present in the composition burned. The method involves the burning of a sample in a pressurized oxygen atmosphere within a closed vessel which retains all the combustion products. The organic compounds are oxidized to carbon dioxide and water, while other volatile gaseous elements are absorbed in water placed in the bottom of the bomb. This solution then can be analyzed for specific elements. The Parr oxygen bomb has also been used to determine t elements such arsenic, mercury, phosphorous, selenium, boron and some other trace elements.
The use of oxygen bombs, such as the Parr bomb, is well-known to those of ordinary skill in he art of the analysis of crude oils for iodine and other elements and is described in the ASTM Standards at ASTM 144-64 (reapproved 1981). The manufacturer of the Parr bomb, the Parr Instruments Company of Moline, Ill., publishes literature describing the various models of Parr bomb and their methods of use. However, Parr's largest commercial bomb has only a 10 gram capacity so that, if an element desired to be liberated is only present in trace amounts, then several thousand combustions and recoveries of the element.must be performed.
Parr bomb combustion techniques generally entail placing small quantities of oil, about 10 grams, in a sealed vessel along with 10 grams of water and about 1 ml of 1 molar sodium bisulfite. The vessel is then charged with several hundred pounds per square inch of oxygen and the oil is ignited. When combustion is complete, the vessel is cooled so that substantially all the water inside condenses. Some of the liberated iodine then enters the water solution by diffusion and reacts to form a salt. When the vessel is opened, any undissolved iodine, which often comprises up to about 50% of the iodine, escapes along with the products of combustion.
This procedure is time consuming and requires the use of relatively expensive laboratory manpower to perform the repetitive tasks of loading the bomb, combustion, cooling and recovery of the dissolved element. Further, the Parr bomb generally suffers from the disadvantage that recovery of the iodine liberated by combustion is not substantially complete--a large proportion of iodine is unrecovered and lost in the escaping gaseous combustion products. This inefficient recovery of iodine contributes to the number of batches of crude oil that must be burned to obtain a sample of iodine large enough for reliable analytical testing to determine the age of the crude oil.
The Parr bomb batch size cannot safely be increased beyond the 10 grams stipulated because O-rings used to seal the bomb once it is loaded tend to weaken as a result of the heat generated by combustion. This often results in leakage and loss of the combustion gases and the liberated iodine.
The concurrently used combustion techniques therefor suffer from several inherent disadvantages. Firstly, large amounts of oil must be incinerated in small batches in order to recover detectable amounts of the sought-for element. For example, it may be necessary to burn as much as about 100 liters of oil to recover sufficient iodine for testing. Given the small maximum size of the combustion bombs, the production of such a quantity of iodine may require several months. However, in many instances, time is of the essence. It is therefore desirable to develop a process which does not require such lengthy time delays. Secondly, the capture of iodine by diffusion into water is inefficient. A relatively high proportion of the iodine liberated is lost with the escaping combustion gases when the vessel is opened. It would be desirable to develop a fast, easy to operate, safe process which allows the recovery of a high proportion of the liberated iodine.